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United States Patent |
6,039,115
|
Mills
|
March 21, 2000
|
Safety coupling for rotary pump
Abstract
A safety coupling for preventing backspin at excessive speeds of a torque
transmitting drive string which stores reactive torque due to torsional
stress. The safety coupling includes a rotatable driving member to be
coupled with a rotatable driven member to be coupled with the driving
string for axial rotation therewith. The driven member is movable relative
to the driving member between an engaged position wherein the driving and
driven members are coupled by a torque transfer structure to provide a
positive driving connection between the torque transmitting drive and the
shaft, and a disengaged position wherein the driving and the driven
members are freely rotatable relative to each other so that back-spin of
the torque transmitting drive is prevented. The driven member is biased
into the disengaged position and forced into the engaged position only
during forward rotation of the shaft. To start rotation of the shaft, the
coupling further includes an auxiliary coupling component which transfers
a selected torque between the driving and driven members for start-up of
the shaft from standstill and to force the driven member into the engaged
position. The auxiliary coupling component is disengaged before
potentially dangerous levels of reactive torsion are stored in the shaft,
which prevents potentially hazardous back-spin, should the main coupling
components of the driving and driven members and torque transfer structure
fail.
Inventors:
|
Mills; Robert A. R. (Bragg Creek, CA)
|
Assignee:
|
Kudu Indutries, Inc. (CA)
|
Appl. No.:
|
049900 |
Filed:
|
March 28, 1998 |
Current U.S. Class: |
166/68.5; 166/76.1; 188/82.1 |
Intern'l Class: |
E21B 043/00; F16D 009/00 |
Field of Search: |
166/68,68.5,78.1,76.1
192/104 C
188/82.1,82.5
418/48
|
References Cited
U.S. Patent Documents
2514228 | Jul., 1950 | Dodge | 192/104.
|
4687085 | Aug., 1987 | Shimizu et al. | 192/89.
|
4797075 | Jan., 1989 | Edwards et al. | 418/48.
|
4840543 | Jun., 1989 | Geberth, Jr. | 417/223.
|
5151068 | Sep., 1992 | Mann et al. | 475/322.
|
5257685 | Nov., 1993 | Tichiaz et al. | 192/46.
|
5358036 | Oct., 1994 | Mills | 166/68.
|
5358455 | Oct., 1994 | Lundstrom | 475/101.
|
5370179 | Dec., 1994 | Mills | 166/68.
|
5405293 | Apr., 1995 | Severinsson | 464/2.
|
5469950 | Nov., 1995 | Lundstrom et al. | 192/85.
|
5551510 | Sep., 1996 | Mills | 166/68.
|
Foreign Patent Documents |
965253 | Apr., 1975 | CA | 64/20.
|
0 105 789 | Apr., 1984 | EP | .
|
Primary Examiner: Tsay; Frank S.
Attorney, Agent or Firm: Pendorf & Cutliff
Claims
I claim:
1. A safety coupling for releasibly connecting a torque transmitting drive
to a drive string which stores reactive torque due to elastic torsion of
the shaft, the drive string normally being rotated in a forward direction
by the torque transmitting drive, and backspin of the drive string being
caused by the release, upon interruption of power to the torque
transmitting drive, of the reactive torque stored in the drive string, the
safety coupling comprising:
a rotatable driving member to be coupled with the torque transmitting
drive;
a driven member to be coupled with the drive string for rotation therewith;
the driven member being axially slidable relative to the driving member
between an engaged position, wherein the driven member is coupled to the
driving member, and a disengaged position, wherein the driven member is
freely rotatable relative to the driving member;
torque transfer means for releasibly connecting the driven member to the
driving member in torque transmitting relation with each other when the
driven member is in the engaged position;
biasing means for forcing the driven member into the disengaged position at
a preselected biasing force;
clutch actuating means for forcing the driven member into the engaged
position against the biasing force of the biasing means, the actuating
means being automatically deactivated when rotation of the shaft stops or
upon back-spin of the shaft and automatically activated only upon forward
rotation of the shaft; and
auxiliary coupling means for transmitting a selected amount of torque from
the driving member to the driven member when the shaft is at standstill
and the driven member is in the disengaged position, the selected torque
being sufficient to initiate forward rotation of the shaft from standstill
and activation of the clutch actuating means, but smaller than a torque
required to build-up the elastic torsion in the shaft required to create a
potentially hazardous back-spin of the shaft;
whereby the driven member is allowed to freely rotate relative to the
driving member during back-spin of the shaft to prevent back-spin of the
torque transmitting drive during operation of the safety coupling.
2. A safety coupling as defined in claim 1, wherein the clutch actuating
means is hydraulically operated and includes a means for generating
hydraulic operating pressure only when the shaft is rotated in the forward
direction.
3. A safety coupling as defined in claim 2, wherein the means for
generating hydraulic operating pressure is a uni-directional hydraulic
pump.
4. A safety coupling as defined in claim 2, wherein the means for
generating hydraulic operating pressure is a bi-directional hydraulic
pump.
5. A safety coupling as defined in claim 2, wherein the selected torque is
sufficient to rotate the shaft until sufficient hydraulic operating
pressure for activation of the clutch actuation means is built up.
6. A safety coupling as defined in claim 2, wherein the driving and driven
members are concentric sleeves and the clutch actuating means is a
hydraulic actuating chamber positioned at an end of the driven member for
applying the hydraulic operating pressure to the driven member and force
the driven member to the engaged position.
7. A safety coupling as defined in claim 6, wherein the torque transfer
means are a plurality of first and second, complementary locking teeth
respectively positioned on the driving and driven member.
8. A safety arrangement for a drive string which stores reactive torque due
to elastic torsion of the shaft, the drive string normally being rotated
in a forward direction by the torque transmitting drive, and backspin of
the drive string being caused by the release, upon interruption of power
to the torque transmitting drive, of the reactive torque stored in the
drive string, the arrangement comprising
a safety coupling as defined in claim 2; and
a brake disc for mounting on the shaft for rotation with the shaft;
a fluid actuated brake mechanism adapted to engage the brake disc and
retard rotation of the brake disc and the shaft; and
a hydraulic fluid control means for directing the fluid from the pump to
the safety coupling when the shaft turns in the forward direction, and for
directing the hydraulic fluid to the brake mechanism when the shaft stops
turning in the forward direction and stored reactive torque is released
from the shaft under tension resulting in back-spin of the shaft, whereby
the stored torque is safely and controllably released.
9. A safety coupling as defined in claim 1, further comprising a shaft
coupler for concentrically connecting the driven member with the shaft,
the driven member being axially slidable on the shaft coupler and the
shaft coupler and driven member including cooperating means for preventing
rotation of the driven member relative to the shaft coupler while allowing
sliding of the driven member therealong.
10. A safety arrangement for a drive string which stores reactive torque
due to elastic torsion of the shaft, the drive string normally being
rotated in a forward direction by the torque transmitting drive, and
backspin of the drive string being caused by the release, upon
interruption of power to the torque transmitting drive, of the reactive
torque stored in the drive string, the arrangement comprising a safety
coupling as defined in claim 1, the clutch actuating means being
hydraulically operated, in combination with a safety brake arrangement
including a hydraulically actuated brake mechanism to be mounted to the
drive string, and a bi-directional hydraulic pump driven by a member
associated with the drive string in both the engaged and disengaged
positions of the safety coupling, and a hydraulic fluid control means for
selectively supplying pressurized hydraulic fluid from the pump to the
clutch actuating means during forward rotation of the shaft only and to
the brake mechanism only during back-spin of the shaft, whereby upon the
interruption of power to the shaft and the subsequent back-spin thereof,
the safety coupling is disengaged and the back-spin of the shaft slowed
down by the brake mechanism for safe and controlled release of the
reactive torque stored in the shaft.
11. A safety coupling as defined in claim 1, wherein the biasing means is a
helical disconnect spring forcing the driven member into the disengaged
position in a direction parallel to a longitudinal axis of the driven
member.
12. A safety coupling as defined in claim 1, wherein the auxiliary coupling
means includes a ball held adjacent the driving member by a ball housing
and a cooperating ball receiving opening and recess in the driving member
and driven member respectively, and means for forcing the ball into the
opening and recess to connect the driving and driven members for the
transmission of the selected torque, the force of the means for forcing
being selected such that the ball is forced out of the recess in the
driven member upon generation of the torque which would be required for
build-up of the elastic torsion of the shaft required to create a
potentially hazardous back-spin in the shaft, the ball also being forced
out of the recess when the driven member moves from the engaged to the
disengaged position.
13. A safety coupling as defined in claim 12, wherein the opening is shaped
and constructed such that the ball remains disengaged from the recess in
the driven member upon the generation of the torque required for torsion
build-up and during back-spin of the shaft.
14. A safety coupling as defined in claim 13, wherein the housing is
axially slidable on the driving member between a starting position wherein
the ball is engaged in the recess and a safety position wherein the ball
is forced out of the recess and the driven member is in the disengaged
position.
15. A safety coupling as defined in claim 14, wherein the opening is an
elongated slot having a longitudinal axis oriented at an angle of about
45.degree. to the longitudinal axis of the driven and driving members.
16. A safety coupling as defined in claim 12, wherein the auxiliary
coupling means includes a plurality of balls and cooperating openings and
recesses equidistantly positioned about an axis of rotation of the driven
and driving members, and a common ball housing.
17. A safety coupling as defined in claim 12, wherein the means for forcing
the ball into the recess is a spring-loaded ball washer.
Description
FIELD OF THE INVENTION
The present invention relates to rotary drive strings which store reactive
torque. More particularly, the invention relates to drive strings for
rotary pumps, which strings store reactive torque by reason of their large
length and relatively small diameter and a head of fluid which causes the
pump to become a motor when power to the drive string is interrupted.
BACKGROUND OF THE INVENTION
Pumping systems wherein the pump is driven by a drive shaft or drive string
are subject to torsional stresses and the resultant torsional strain
increases with the length of the shaft or string and large amounts of
energy may be stored as torsion in the drive train. Many pumping systems
also store a head of fluid in the production tubing which stores large
amounts of energy in the system, which may be released by reverse rotation
of the drive string when the fluid drains through the pump causing it to
motor backwards. When drive power to the system is interrupted, the
reactive torque is released as backspin and, if an uncontrolled release of
torque occurs, personal injury and/or property damage can result. This is
the case, for example, in deep well down hole rotary pumps such as
progressing cavity pumps. Rotary down hole pumps have been used in water
wells for many years. More recently, especially progressing cavity pumps
have been found well suited for the pumping of viscous or thick fluids
such as crude oil laden with sand. Rotary down hole pumps are generally
driven by sucker rod drive strings which usually have a relatively small
diameter of 3/4 to 11/8 inches. Such drive strings are commonly used in
wells that vary from 1,500' to 6,000' in depth, 3,000' being a common
average.
Progressing cavity pumps include a stator which is attached to a production
tubing at the bottom of a well and a rotor which is attached to a bottom
end of the drive string. The elongated drive string is subject to
considerable torsional force which increases with the viscosity of the
liquid being pumped and the displacement of the pump. This torsional force
is stored in the elongated drive string as reactive torque. Forty to sixty
revolutions of torsion can be stored in the drive string with a
high-capacity pump in normal operation in a 1000 m deep well. If the pump
seizes, which is a frequent occurrence in viscous, sand-laden crude oil,
several hundreds of revolutions of torsion may be stored before the prime
mover stops. When power is interrupted to the drive string, the reactive
torque is released. Unless the release of reactive torque is controlled,
violent backspin of the drive string will result, especially if an
electric motor is used as a power source, which, when disconnected from
the power supply, offers almost no resistance to reverse rotation. This
can lead to costly and undesirable damage to equipment and/or personal
injury to workmen in the vicinity of the equipment.
Various braking systems have been developed which provide for a controlled
release of the reactive torque stored in the drive string of down hole
rotary pumps upon interruption of drive power to the drive string. These
are fluid brakes or hydraulically operated brakes, such as disclosed in
commonly owned U.S. Pat. No. 5,358,036, the complete disclosure of which
is incorporated herein by reference, or other braking systems which
operate on centrifugal braking principles (U.S. Pat. Nos. 4,216,848 to
Toyohisa Shiomdaira; U.S. Pat. No. 4,797,075 to Wallace L. Edwards et al.;
and U.S. Pat. No. 4,993,276 to Wallace L. Edwards). However, although
these braking systems are all intended to control the release of reactive
torque stored in the drive train, they are all subject to possible failure
due to wear, exposure to the elements, accidental damage, etc. If power to
the drive string is interrupted and the braking system fails, uncontrolled
back-spin of the drive string will occur which can result in damage not
only to the drive train but also to the braking system. Even more
importantly, maintenance personnel unaware of the braking system failure
and relying on the system to control the release of any reactive torque
stored in the drive string after shut-off, can be severely injured. The
violent, uncontrolled back-spin of the drive string observed in the
absence of braking systems or with improper or damaged braking systems has
led to drive pulleys exploding, drive string free ends breaking off, and
electric drive motors destructing. Thus, a "fail-safe" back-up system is
desired which would prevent damage to the equipment rotating the drive
string and injury to personnel upon back-spin of pump drive strings caused
by the uncontrolled release of reactive torque stored therein.
Brake systems also fail frequently because of the head of fluid in the
tubing. This column of fluid stores a large amount of potential energy,
especially in low productivity wells and wells with low formation
pressure. The fluid usually drains back through the pump causing it to
become a motor which will drive the string backwards for an extended
period of time, typically 15 to 30 minutes. The stored energy must be
absorbed and dissipated by the brake which is, therefore, subjected to
extreme heat and wear, if it does not have adequate capacity.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a relatively simple and
reliable safety coupling for permitting rotation of a drive string in a
first direction and for automatic disconnection of the shaft upon stoppage
and subsequent back-spin of the shaft caused by the release of torsion
stored in the drive string when power to the drive string is interrupted.
It is a further object of the invention to provide a safety coupling for
elongated pump drive strings which automatically disconnects the drive
string from the power source upon stoppage and subsequent back-spin of the
drive string due to the release of reactive torque stored in the elongated
drive string, when power to the drive string is interrupted.
It is yet another object of the invention to provide a safety coupling for
automatically disconnecting the drive string of a down hole rotary pump
when power to the drive string is interrupted.
It is an object of the invention that the safety coupling be "fail-safe",
i.e., it will disconnect when the means which operates the safety coupling
and/or the brake fails.
It is a further object of the invention to provide an automatic means of
reconnecting the drive string to the drive means upon re-start.
It is an additional object of the invention to provide a safety arrangement
for a rotary shaft which stores reactive torque due to elastic torsion of
the shaft, which arrangement includes, in combination, a safety coupling
in accordance with the invention and a safety disk brake, which are
operated by a common actuating means automatically operating the safety
coupling to connect the shaft to a power source upon forward rotation of
the shaft and operating the disk brake simultaneous to disengagement of
the safety coupling upon back-spin of the shaft to simultaneously
disconnect the shaft from the power source and slow down the back-spin of
the shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further described by way of example only and with
reference to the following drawings, wherein:
FIG. 1 is a schematic side elevational view of a rotary down hole pump
arrangement which includes a safety coupling in accordance with the
invention as well as a safety disc brake;
FIGS. 2A and 3A show axial cross-section through the preferred embodiment
of a safety coupling in accordance with the invention, the safety coupling
being shown in the engaged condition in FIG. 2A and in the disengaged
condition in FIG. 3A;
FIGS. 2B and 3B are side elevational views of the embodiment shown in FIGS.
2A and 3A respectively; and
FIG. 4 is an axial cross-sectional view of the drivehead of the rotary down
hole pumping arrangement shown in FIG. 1 taken along the same plane as the
cross-section of FIG. 2A and illustrating the polished rod and slip shaft
as they extend through the drivehead and further including a
uni-directional disc brake operationally linked with the safety coupling
illustrated in FIGS. 2A and 2B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The safety coupling in accordance with the invention is useful for
disconnecting elongated drive strings, which store reactive torque due to
torsional stress, from a torque transmitting drive upon excessive
counter-rotation or back-spin of the drive string, such as the sucker rod
strings used to drive rotary down hole pumps. The safety coupling is not
limited to that application and may be used in conjunction with a shaft
which transmits reactive torque and back-spins when power is interrupted
to the shaft. For purposes of illustration only, the safety coupling in
accordance with the invention is described in conjunction with a drivehead
suitable for use with a sucker rod string typically used to drive a rotary
down hole pump such as a progressing cavity pump.
One preferred application of a safety coupling in accordance with the
invention is illustrated in FIG. 1 which shows a rotary down hole pump
drivehead assembly 10 used for the operation of a progressing cavity down
hole pump 12 that includes a stator 14 and a rotor 16. The rotor 16 is
connected with the drivehead assembly 10 by a drive string 18 which is
rotatable in a production tubing or well casing 20. The rotary drive
assembly 10 includes a drivehead 30, the construction of which will be
discussed in detail below with reference to FIG. 4. The drivehead 30
includes a drive spindle 50 which is rotatably supported in the drivehead
30 in a manner well-known in the art (see commonly owned U.S. Pat. No.
5,370,179), a safety coupling 100 in accordance with the present invention
which is connected to the drive spindle, and a brake mechanism 200 to slow
down back-spin of the shaft. A mounting frame 32 which is screwed to the
top end of a well head assembly 34 supports the safety brake mechanism
200. The safety coupling 100 in accordance with the invention is mounted
above the brake mechanism 200 by way of a housing 102 and a yoke 104. The
brake mechanism is preferably a uni-directional shaft brake such as
disclosed in commonly owned U.S. Pat. No. 5,358,036, the complete
disclosure of which is herewith incorporated by reference. The drive
string 18 includes a slip shaft 36, preferably of hexagonal cross-section
(see FIGS. 1 and 4), which extends through and is rotated by drivehead 30
as will be described below. The drive string 18 is suspended from the
drivehead 30 by way of a clamp 38 which is shaped to accommodate an end of
the slip shaft 36 that protrudes upward from the drive spindle 50. The
clamp 38 is fastened to the slip shaft 36 above the drive spindle 50 and
rests on a top surface thereof. Torque is transmitted to the drive string
18 through a torque transmitting drive 22 which includes an electric motor
40, a drive pulley 41, drive belts 46, a driven pulley 43 and the safety
coupling 100. The drive pulley 41 is mounted to a drive axis 42 of the
motor 40 and the driven pulley is freely rotatably mounted around the
drive spindle 50 and connectable to the drive string for torque
transmission by a safety coupling 100 as will be described in detail below
with reference to FIGS. 2A, 2B, 3A, 3B, and 4. Multiple V-belts 46 are
tensioned around the drive and driven pulleys 41 and 43 and transfer
torque from the motor 40 to the safety coupling 100. The mounting of the
safety coupling 100 on the drive spindle 50 and the detailed construction
of the safety coupling will be discussed in detail below. Alternatively,
the torque transmitting drive 22 may be a right angle gear drive powered
by an internal combustion engine (not illustrated) or a comparable torque
producing power source, in a manner well known in the art.
FIG. 2A shows a cross-section of the preferred embodiment of the safety
coupling of the invention in the engaged and running position. From the
inside out, it consists of a shaft coupler 51 for connection to the
protruding top of the drive spindle 50. This feature allows for the weight
of the drive string 18 to be suspended from the top of the drive spindle
by means of rod clamp 38 (see FIG. 1) resting on the top end of the
spindle in a manner well-known in the art. Rotation of the drive string 18
relative to the spindle 50 is prevented either by a key or a hexagonal
profile in the drive spindle 50 wherein the hexagonal shaft 36 (see FIGS.
1 and 4) is fittingly received. The shaft coupler 51 is prevented from
rotating on the spindle 50 by a key 55. A sliding sleeve 110 axially
slidably and concentrically surrounds the shaft coupler 51. The sliding
sleeve 110 is rotationally connected to the shaft coupler for torque
transmission during forward rotation by multiple splines 112a on shaft
coupler 51 equidistantly distributed about the central axis of rotation
and respectively received in complementary receiver 112b in sliding sleeve
110. At its top end 113, the sliding sleeve 110 is provided with a
multitude of first locking teeth 116 (see FIG. 2B). A carrier sleeve 120
concentrically surrounds the sliding sleeve and carries the torque
transmitting pulley 43 of the torque transmitting drive 22 (see FIG. 1).
The driven pulley 43 is mounted on a flange 115 affixed to the top end of
the carrier sleeve 120. Second locking teeth 122 (FIG. 2B) in the form of
a spur gear 117 are also affixed to the top end of the carrier sleeve 120
and are complementary to and interlock with the first locking teeth 116 of
the sliding sleeve 110, when the sliding sleeve is in the engaged position
as shown in FIG. 2A. The first and second locking teeth 116, 122 are of
saw tooth shape and provide the preferred torque transfer means according
to the invention for releasibly connecting the driving member of the
safety clutch, the carrier sleeve 120, with the driven member of the
safety clutch, the sliding sleeve 110. The latter can slide vertically a
sufficient distance to engage and disengage the first and second locking
teeth 116, 122. The sliding sleeve 110 is biased into the disengaged
position by biasing means, in this embodiment a plurality of axially
acting, helical disconnect springs 124 positioned between a radial
shoulder 126 of the shaft coupler 51 and an axially opposite, second
radial shoulder 128 of the sliding sleeve 110. The shaft coupler 51 is
concentrically rotably supported in a stationary housing 130 ny axial
thrust bearings 134. The carrier sleeve 120 is concentrically, rotatably
supported in the stationary housing 130 by way of radially acting tapered
roller bearings 132. The housing 130 is concentrically mounted on the
drivehead. The housing 130, shaft coupler 51 and carrier sleeve 120 define
an annular oil-filled, hydraulic actuating chamber 140 directly adjacent
the bottom end 115 of the sliding sleeve 110. The actuating chamber 140 is
sealed to ambient by a first lip seal 142 positioned between the shaft
coupler 51 and sliding sleeve 110, a second lip seal 144 positioned
between the shaft coupler 51 and the housing 130 and a third lip seal 145
positioned between the carrier sleeve 120 and the housing 130. Thus, the
sliding sleeve 110 acts as a hydraulic piston and is moved axially upward
against the force of the disconnect springs 124 upon pressurization of the
actuating chamber 140. Pressurized hydraulic fluid is supplied to the
actuating chamber 140 through a radial bore 148 provided in the housing
130 and from a hydraulic pump 57 (see FIGS. 1 and 4), which will be
discussed in more detail below and which produces pressurized fluid during
forward rotation of the spindle 50. The pump 57 is preferably the
lubricating oil pump included in conventional rotating well-head
arrangements (see commonly-owned U.S. Pat. No. 5,358,036).
Above the housing 130 and below its top end, the carrier sleeve 120 is
provided with a number of circumferentially equidistantly spaced elongated
slots 150 (see also FIGS. 2B, and 3B, one shown in broken lines), which
are angled at 45' to the axis of rotation. An annular ball housing 152
closely surrounds the carrier sleeve 120 in the region of the slots 150
and houses a number of balls 154 which are positioned one each in and fit
into the slots 150. The balls 154 are forced into the slots 150 by way of
spring-loaded ball washers 156. The sliding sleeve 110 is provided with a
number of circular detents 158 for respectively receiving the balls 154.
The detents are also circumferentially equidistantly positioned and are
positioned in axial direction such that they are located at the same
height as the upper end of the slots 150 when the sliding sleeve 110 is in
the coupled position. The ball housing 152 is slidably sealed against the
carrier sleeve 120 by O-rings 135.
During operation, when power is supplied to the drive string 18 and it is
rotated forward during pumping, the hydraulic actuating chamber 140 is
pressurized and the sliding sleeve 110 is in the engaged position (see
FIG. 2A) wherein the first and second locking teeth 116, 122 are engaged
so that torque is transmitted from the pulley 43 to the drive string 18 by
way of the locking teeth 116, 122 coupling the carrier sleeve 120 and the
sliding sleeve 110, the splines 112 connecting the sliding sleeve 110 and
the shaft coupler 51, and the key 55 locking the shaft coupler 51 to the
spindle 50 which engages the drive string 18 as described above. The balls
154 are fully engaged in the detents 158 (see also FIG. 2B), but do not
transmit any torque, since the locking teeth 116, 122 are engaged and
prevent rotation of the carrier sleeve 120 relative to the sliding sleeve
110. Pressurized hydraulic fluid is constantly supplied to the actuating
chamber 140 during operation. The housing 130 is grease packed for
lubrication of the bearings. The capacity of the pump is selected so that
it always supplies pressurized hydraulic fluid during forward rotation of
the shaft to create sufficient force on the sliding sleeve 110 to more
than counterbalance the resetting force of the disconnect springs 124.
When power is interrupted or the drivehead starts to back-spin for any
reason, the pressure in the actuating chamber 140 immediately drops to 0
because the hydraulic pump 57 only supplies the pressurized hydraulic oil
during forward rotation of the drive string 18 which is driven off a
drivehead rotating component, in this embodiment the spindle 50, and does
not produce hydraulic pressure when it turns backwards. As a result, the
pressure in the actuating chamber 140 drops and the resetting force of the
disconnect springs 124 overcomes the friction between the mating locking
teeth 116, 122 and forces the sliding sleeve 110 down into the uncoupled
position (shown in FIG. 3A), wherein the locking teeth 116, 122 are
disengaged. Simultaneously, the balls 154 are forced out of the detents
158, since the sliding sleeve 110 is forced vertically downward, guided by
the vertical tooth surfaces 119 (see FIGS. 2B and 3B) of the locking teeth
116, 122. The sliding sleeve 110, shaft coupler 51, spindle 50 and drive
string 18 then rotate backwards while the driven pulley 43 remains
stationary or rotates at a slow speed because, although it is disconnected
from the sliding sleeve 110, there is inertia in the large driven pulley
43. The balls 154 in that position of the sliding sleeve 110 are free to
rotate. FIG. 3B illustrates the position of the balls 154 relative to the
slots 150 and detents 158 (shown in broken lines). The balls 154 act as a
bearing between the sliding sleeve 110 and the carrier sleeve 120 in the
uncoupled position of the sliding sleeve. The force of the ball washer
springs 157 creates enough drag that the balls 132 are forced up the
inclined ramp provided by the angled slots 150, and the ball housing 152
remains in the upper position during the backspin. Thus, the safety clutch
of the invention provides an immediate disconnection of the torque
transmitting drive 22 and the driven pulley 43 (FIG. 1) from the drive
string 18 upon stopping and subsequent backspin of the drive string due to
interruption of power to the shaft. Furthermore, the safety coupling of
the invention provides a fail-safe system, since the disconnect springs
124 are always energized, and will operate independently of the hydraulic
system. Thus, the safety clutch of the invention will also reliably
prevent damage to the torque transmitting drive when the hydraulic oil is
lost from the hydraulic system. The hydraulic oil preferably is also the
lubricating oil for the drivehead. Therefore, when the lubricating oil is
lost, the hydraulic pressure drops to 0 and the clutch will disengage
thereby protecting the drivehead.
Once the drive string 18 has come to rest after complete release of the
elastic torsion therein, the safety clutch of the invention can be
automatically re-engaged to recommence the pumping operation. This is
advantageous, since down hole rotary pumps are often used in remote areas
so that manual re-engagement of the drive system would not be economical,
especially when a large number of pumps are affected by a general power
outage. To re-engage the clutch after the drive string 18 comes to rest,
the electric motor 40 is jogged backwards. This is accomplished
automatically upon start-up with a circuitry known in the art and
available from Kudu Industries, Inc., Calgary. The inertia of the ball
housing and the low friction on the carrier sleeve 120 coupled with the
friction of the balls 154 and the sliding sleeve 110, the spring-loaded
ball washers 156 and the respectively associated slot 150, which is at an
angle pushing the balls down, causes the balls to travel to the bottom end
of the slots 150 in the carrier sleeve 120, shifting the ball housing 152
downwards (not shown). In this position, the balls are engaged in the
detents 158. The locking teeth 116, 122 are still disengaged, since the
sliding sleeve 110 is in the disengaged position. The electric motor 40 is
then rotated forward. The balls 154 will transmit enough torque from the
carrier sleeve 120 to the sliding sleeve 110 to initiate rotation of the
shaft 18. This results in pressure build-up in the hydraulic system. The
force of the ball washer springs 157 is selected such that the balls 154
are forced into the detents 158 at sufficient force to transmit enough
torque for the hydraulic pressure to buildup. The hydraulic pressure in
the chamber 140 overcomes the force of the disconnect springs 124 and
forces the sliding sleeve 110 upwards. The sliding sleeve 110 rotates with
respect to the carrier sleeve 120 as it moves upwards so that the balls
154 remain in the detents 158 and follow the slots 150. The ball housing
58 is thus shifted upwards to the position shown in FIGS. 2B and 3B. The
back slope of engagement teeth 116 and 122 is the same angle as the slots
150 and the engagement teeth 116 and 122 are almost the same height as the
vertical travel of the balls 154 to assist in this relative rotation
between the sliding sleeve 110 and the carrier sleeve 120, and to provide
for a smooth engagement. However, the ball washer springs 157 are not
sufficiently strong to hold the balls 154 in the detents 158 for rotation
of the pump 12 (see FIG. 1). To the contrary, the force of the ball washer
springs 157 is selected such that balls 154 would be forced out of the
detents 158 by the carrier sleeve 120 before the torque increased enough
to create a potentially hazardous back-spin in the event that the
engagement teeth 116 and 122 were not engaged by hydraulic pressure upon
start-up. This prevents damage to the drivehead components when the
hydraulic system is malfunctioning or the hydraulic oil has been lost.
Thus, the safety coupling of the invention provides two separate clutch
arrangements, the main clutch arrangement including sliding sleeve 110,
carrier sleeve 120 and locking teeth 116, 122 for transition of full
torque during operation, and the auxiliary clutch arrangement including
balls 154, carrier sleeve slots 150 and sliding sleeve detents 158, which
transmit sufficient torque upon start-up to build up hydraulic pressure
for engagement of the main clutch arrangement, but not sufficient torque
for a build-up of a potentially hazardous back-spin, should the main
clutch arrangement fail. Furthermore, failure of the auxiliary clutch
arrangement will not lead to damage of the drivehead and its components,
since the safety coupling will simply not engage upon start-up of the
electric motor 40.
In a preferred safety arrangement in accordance with the invention, the
safety coupling 100 is combined with a safety brake 200 as shown in FIGS.
1 and 4, whereby both the coupling and the brake are hydraulically
operated and supplied with pressurized hydraulic fluid from a common
hydraulic pump 57. The safety brake is a hydraulically actuated disc brake
including a brake disc 202 mounted on the drivehead hollow shaft or
spindle 50, and a brake caliper 206. The brake caliper is preferably of a
type commercially available from MICO INCORPORATED, North Markoto, Minn.,
U.S.A. It is mounted to the drivehead 30 in a manner recommended by the
manufacturer. Brake pads 204 are movably supported in the caliper 206 for
engagement of the brake disc 202 upon supply of pressurized hydraulic
fluid thereto. The hydraulic pump 57 is a bidirectional pump which is
driven off the drivehead spindle 50 by means of a pair of gears 212, 214
mounted on the pump shaft 216 and the drivehead spindle 50 respectively.
Pressurized hydraulic fluid is supplied selectively to either one of the
coupling 100 and the brake 200 by a fluid manifold 220.
During forward rotation of the shaft, pressurized hydraulic fluid produced
by the pump is directed by the manifold 220 to the actuating chamber 140
of the coupling through supply line 222. The drivehead 30 also functions
as a hydraulic fluid reservoir from which the pump 57 draws the fluid to
be pressurized. At the same time, this ensures proper lubrication of the
pump and the associated drive and bearing components.
During back-spin of the shaft, no hydraulic fluid is supplied to the
coupling 100. Pressurized fluid produced by the pump 57 is directed by
manifold 220 to the brake caliper 206 of the brake 200 to force brake pads
204 against brake disc 202. The faster the back-spin, the higher the
pressure created by the pump and the larger the brake force of the brake
200. Thus, the coupling 100 is automatically disengaged upon stoppage or
back-spin of the shaft and the release of reactive torque in the shaft is
controlled by the brake 200. The resulting arrangement is failsafe in that
excessive back-spin of the torque transmitting drive components is
prevented at all times even if the brake 200 should fail or the hydraulic
fluid is lost.
Changes and modifications in the specifically described embodiments can be
carried out without departing from the scope of the invention which is
intended to be limited only by the scope of the appended claims.
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